Ferrosilicon product and method of continuously producing the same.



H. C. HARRISON.

FERROSILICON PRODUCT AND METHOD OF CONTINUOUSLY PRODUCING THE SAME.

APPLICATION FILED 050.1, 1909. RENEWED SEPT. 1, 1914.

1 1 34, 1 28. Pate Apr. 6, 1915..

um M70 960? WW V T'TKTF f? wi l or if; a we :1 WWW Malawi a .iinahll n Mid in all/rho I-IERBEBT CI-TATJZEEUN HARE-ISON, OF LOCKJPORT, NEVJ YURI i, ASSIGNOR, MESNE ASSIGNMENTS, T9 ELECTRQ METALLURGICAL CGI'JIPANY, A COEtPORATI-ON 015 WEST VIRGINEA,

FEE-BOSILIGON PBGDUCT AND Specification of Letters Patent.

METHOD OF CONTINUOUSLY PEUDUCING THE SAIYZE.

7, IL 151 Baton A r. o, 915.

Application filed Ziecember l, 1999, Serial No. 530,787. Renewed September 1, 1914. Serial No. 859,722.

To aZZ whom it may concern:

Be it known that l, HERBERT G. HAR- RISON, a subject of His Majesty the King of Great Britain, residing at Lockport, in the county of Niagara and State of New York, have invented certain new and useful improvements in l errosilicon Products and Methods oi Continuously Producing the Same; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the artto which it appertains to make and use the same.

This invention relates to crystalline ferro silicon products and methods of producing silicides of iron economically and continuously of any desired silicon content, and has for its object in particular the production in a crystalline form of a silicide of iron which will correspond substantially to the formula Fefii, or 54.2 per cent. silicon.

lVith these objects in View the invention consists in the novel method and product hereinafter more fully disclosed and particularly pointed out in the claims.

Referring to the drawing forming a part or this specification, in which the figure illustrates a conventional form of an electric furnace suitable for carrying out the process, and for producing the product, 1 represents suitable electrodes, 2 the furnace, 3 the charge, and i the molten product.

In carrying out the method the ferrosilicon charge is so proportioned in the well known manner that the total silicon content of the silica combined with the iron will form a silicide or alloy of iron and silicon of the desired silicon content. lhis charge is then heated in an electric furnace in the usual way, the heat energy entering the furnace being so proportioned to the size of the furnace that practically all the silicon content of the mined silica and iron will unite with the iron, either chemically or as an alloy.

For any particular furnace the amount of energy necessary can be conveniently determined by experience. llut a better way is to increase the input of power from an amount known to he too small up to a point at which the products of the reaction appear combined Without an appreciable loss. of materiel. other that of Carlson.

To illustrate the principle involved, attention is called to the fact that even though chemically the furnace charge may be correctly proportioned, yet if the power input to the furnace is'insuliicient, the silica will be reduced more slowly than the iron that is melted out of the charge material can find its way to the molten bath at the furnace bottom; and, therefore, a product will be yielded in which all the iron will appear but not all the silicon which should have resulted from the charge. If on the other hand too much power is employed the result will be to waste the silicon by volatilization, and again the maximum yield of silicon will not be obtained. Therefore, the principle underlying the method requires that only sufficient power be employed to reduce the silicon just so fast and no faster than the iron which is melted out of the charge material finds its way to the bottom of the furnace. complied with can a furnace be continuously employed to make any desired uniform per centage of material. But of course, the same result, at a lower efiiciency, can be obtained where the power is incorrectly proportioned if one is willing to waste the reduced silicon by volatilization from a charge containing more silicon than is necessary, or if he is willing to continually correct by an omission of iron and an increase of carbon the tendcncy that a deficiency of power has to reduce the silicon content of the product.

Every design or" furnace, or" course, (llfi QIS in the amount of power necessary for the best results owing to the special conditions in .*olved, the rate of radiation of heat, and the spacing and size of the electrodes; so the best that can be done is to first desigi a furnace from the best knowledge previously obtained from practice, and afterward ascertain by trial and error What a mountot power will effect the total reaction without undue loss of silicon by volatilize,- tion. Within rather wide limits the voltage of the current employed may be altered, and this will entail either a different spacing of the electrode, or in cases where this is im possible it will compel a variation in the excess of fixed carbon in the charge over that theoretically needed to eiiect reduction of the silicon. .lt will, therefore, be clear Only when these conditions are that it is exceedingly difficult if not impossible to give a specific example accompanied by accurate data, but at the same time, those skilled in this art will find no diiiiculty in carrying out this invention if they will bear in mind that :In' the manufacture of ferrosilicon from silica, quartz, scrap iron or steel, and carbon in the form of charcoal, or of charcoal and coke, the following gen eral principles have to be observed to obtain amaximum efiiciency; and that most of these rules although applicable in general" to the manufacture of alloys in an electric furna'ce, are yet more particularly applicable where, as in the case of ferrosilicon the more volatile constituent of the resulting product is reduced from the ore, and is itself volatile when compared with the other con-.

stit-uents of the alloy, which may be comparatively stable metals at the temperature to which they are subjected in the furnace. The principles in question are (1) The silicon and iron should be proportioned in the charge in the same ratio that they are required to be proportioned in ing the zone of reduction as low as may be practically safe.

(3) The electrical energy fed into any given furnace will vary directly with the silicon percentage of the alloy required to'be made, as also Wlll the temperature attained inside the furnace, and consequently the temperature of the resulting product. That is to say, for every given percentage of 'silie con in the resulting alloy under the working conditions outlined above, there will be a critical temperature at which the metal will run from the tap hole and which tern erature increases as the .silicon content 0 the alloy increases. Heat. conditions of the furnace must always be such that protecting walls form themselves out of the slag and semi-reduced charge material of such a thickness as to be practically independent of the containing furnace walls, and yet are of such thickness as to render the tapping of the furnace a simple and expeditious operation.

(4) To a considerable extent the iron will be melted out of the charge from zones of comparatively low temperature and which are higher up in the furnace than where the conditions-are such as to reduce the silica; and the iron so melted will drip downward collecting the reduced silicon, and acting as a silicon carrier up to the point of the saturation of iron with silicon. If this saturation point occurs at the silicon percentage of approximately 53.5 per cent. to 54 per cent. silicon, a chemical compound corresponding to the formula Fe Si may be isolated in definite crystalline form. Up to this point the amount of silicon contained in the product is constant under correct Working conditions for any given amount of power put into the furnace irrespective of whether the alloy produced contains much or little silicon, be tween the limits of an alloy containing 30 percent. to 54 per cent. silicon. -And up to this saturation point when working with pure materials the product is solid and c0- herent, but immediately beyond this point the material disintegrates, showing that the iron has been supersaturated with silicon. At higher percentages of silicon the product again becomes solid, practically pure silicon being] very tough and solid. An abrupt change in the color of the alloy occurs approximately at the percentage of 54 per cent. silicon. Below this the alloy is of a bright steel color, while above this point the alloy assumes the bluish gray color characteristic of silicon. Above the limit of 54 per cent. silicon in an alloy the silicon appearing in the product under correct working conditions of manufacture for any iven amount of power .put into the furnace decreases continuously in proportion as the silicon percentage of the alloy increases, showing that when the quantity of iron acting as a carrier is small, an excessive loss of silicon occurs by volatilization.

In the particular case of the manufacture of a crystalline product corresponding to the formula Fe Si the charge is so proportioned that the silicide resulting should be of silicon content between 53 per cent. and 54.5 per cent. silicon; and if the power in put to the furnace is properly adjusted to the size of the furnace, and the carbon for reductlon urposes accurately proportioned to the wor 'ng conditions of the furnace the critical temperature suitable for a continuous production will be attained in the furnace; and a practically pure crystalline product may be continuously tapped out, 'in which when cooled and broken up are found matrices filled with bright, shining, hard brittle crystals, in a plateform which analyze about 54.2 per cent. silicon, depending upon whether the particular matrix selected is relatively rich or poor in silicon. If the matrices are melted and permitted to cool,

tends to show that they have a higher melting point than the ferrosilicon alloys on these crystals invariably solidify first which messes either side of the same. poorer matrices probably contain about .7 per cent. of impurities, While crystals from rich matrices analyze practically &2 per cent. silicon, corresponding to the formula. Fe Si taking the atomic weight of iron as 55.9, and of silicon as 28.4. These crystals are, of course, a much purer compound of iron and silicon than the usual commercial alloys, and therefore, they oiler special advantages in metallurgy, over the regular alloys of say to per cent. silicon. They contain less carbon and phosphorus than do such alloys, and having a slightly higher melting point than the impurer alloys they are less lilrely to lose their silicon during the process of purifying the metal. In other WOIClS, it is Well recognized in metallurgy, that it is very important to obtain the purest product possible and it is obvious that a crystalline product of this nature is purer than the chance alloys heretofore employed. it is also probable that When the silicon is liberated from a chemical compound, as is the case here, it being in a nascent state, so to speak, that it will be more active chemically in the molten iron than would be the case were it merely liberated from alloy.

in many cases the crystals need not be separated from their matrices before being used, for the mixture consisting of the crystals and matrices can always be depended on to analyze substantially between. 53 and 54.5 per cent. of silicon, which is a product sufiiciently pure for many purposes.

if the charge is inadeup so as to produce other than 53 to 54:.5 per cent. of silicon the crystal product becomes less, and it can be made so Widely different from this silicon content that the crystal product Will disappear entirely.

(it course, it is understood that those skilled in the art may vary the details of procedure Without departing from the spirit of my invention, and, therefore, 1 do not wish to be limited to such details except as may be required by the claims.

- That I claim is i' 1. The method of continuously producing ferrosilicon or a required; proportion of silicon and iron, Which consists in suitably proportioning the silicon content of the charge material to the iron content of the charge material in the same ratio as is required by the resulting product; supplying carbon in excess of that required to theoretically effect a reduction of the silica and other oxidizable constituents of the charge, but suflicient to prevent the charge material from bridging between the electrodes, thereby causing a tree feeding of the charge material to the zone of reduction and in causing the iron to be melted out of the charge material only so tastes the silica is reduced Crystals from the and to gravitate to the reduced silicon, substantially as described.

2. The method of continuously producing tcrrosilicon oi a required proportion of silicon and iron, yvhich consists in proportioning the silicon content of the charge material to the iron content oi the charge material in the chemical ratio required by the resulting product; supplying carbon in ex cess of that required to theoretically efiect a reduction of the oxidizable constituents of the charge, but only in an amount suliicient to prevent the charge material from bridging between the electrodes, thereby causing a free feeding of the charge material to the zone of reduction and at the same time avoiding an undue rise of temperature in said Zone and in causing the iron to be melted out of the charge material only so fast as the silicon is produced, to gravitate to the reduced silicon and to act as a carrier of silicon up to the point of saturation of iron with silicon, substantially as described.

3. The method of producing continuously ferrosilicon of a definite proportion of silicon and iron, which consists in suitably proportioning the size of the furnace With respect to the heat energy to be used and to the percentage of silicon required in the finished product; in maintaining a maximum zone 01"" reduction at substantially the lowest point of the charge; causing the iron to be melted out of the charge material from a point above the said maximum zone and to gravitate to the molten bath below said zone only so fast as the silicon is reduced, substantially as described.

l. The method of producing continuously terrosilicon of a dethoite proportion of silicon and iron, which consists in proportioning the size of the furnace to the electrical energy required to be employed and inversely to the silicon percentage of the required alloy; maintaining the maximum zone of reduction in the furnace at substantially the lowest portion of the charge material; permitting the iron to be melted of the charge material above said maximum. zone and to gravitate to the molten bath the bottom. of the furnace at a rate bearing the same ratio to the rate of silicon reduction that the quantity of iron in the charge material bears to the quantity of silicon in the charge material, substantially as described.

5. The method of producing continuously ferrosilicon ofany definite required propor tion of silicon and iron which consists in suitably controlling the temperature in the furnace for any required percentage of silicon alloy and in such a manner as to produce a critical temperature iii the zone of reduction; increasing said temperature as the silicon content of the alloy produced increases; in determining at What point dur- In testimony whereof I afiix my signaing the increase of temperature the constitture in presence of two Witnesses.

uents of the resulting product bear to each other the same ratio that they bore in the HERBERT CHAMPION HARRISON charge material; and in maintaining said Witnesses: temperature at that point, substantially as L. B. PATTERSON, described. HARRIETT G. HUSTON. 

